JSFiddle - React, Tailwind, and code Playground

HTML

<div id="left"></div>
<div id="content"></div>

CSS

#left {
    background: red;
    float: left;
    height: 20px;
    width: 20px;
}

#content {
    background: yellow;
    height: 100px;
    margin: 0 auto;
    width: 200px;
}

JavaScript

var contentWidth = $('#content').width();
var leftWidth = $('#left').width();

$('#content').click(function() {
   var allwidth = contentWidth + leftWidth*2;
    var windowWidth = window.innerWidth;
    alert(allwidth);
    alert(windowWidth);
});

window.onresize = function(event) {
    var windowWidth = window.innerWidth;
    
    if (windowWidth <= (contentWidth + (leftWidth*2))) {
        $('#content').css('margin-top', leftWidth);
    } else {
        $('#content').css('margin-top', 'auto')
    }
}